As there are a constantly growing number of mobile data services, spectrum resources appear more and more insufficient, and a demand for a large number of services may not be satisfied by deploying a network and transmitting the services only over licensed spectrum resources, so transmission may alternatively be deployed over unlicensed spectrum resources in a Long Term Evolution (LTE) system, which is referred to as an Unlicensed LTE (simply U-LTE or LTE-U) system, so as to improve the experience of a user, and to extend the coverage area of the system.
The unlicensed spectrum resources have not been planed for any particular application system, but can be shared by various wireless communication system, e.g., Bluetooth, Wireless Fidelity (WiFi), and other systems, all of which access the shared unlicensed spectrum resources by preempting the resources, so coexistence between LTE-Us deployed by different operators, and between the LTE-Us, and WiFi and other wireless communication systems has been studied as a focus. In the 3GPP, fair coexistence between the LTE-Us, and the WiFi and other wireless communication systems is required to be guaranteed, and an unlicensed frequency band is arranged as a secondary carrier with the assistance of a primary carrier in a licensed frequency band. The technology of Listen Before Talk (LBT) has been accepted by almost all the enterprises as a general mode in which the LTE-Us compete for an access. Essentially in the LBT technology, an 802.11 system operates with the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) mechanism, and a WiFi system preempts a resource in an unlicensed spectrum. Firstly each node listens to a channel, and if the channel becomes idle in a Distributed Inter-Frame Space, then the node will determine the current channel as an idle channel, and then the respective nodes waiting for a channel to access enter a random fallback phase to thereby avoid a number of nodes from colliding over the same resource. Furthermore in order to guarantee unfairness, no node shall preempt a spectrum resource for a long period of time, but if some temporal or amount-of-transmitted-data upper-limit is reached, then the resource will be released for preemption by another device/system.
However there has been absent so far a solution for scheduling over an unlicensed carrier.